Investigations of the biochemical feasibility for mealloprotein nitrosyl formation, nitrosyl transfer, and nitrosylation reactions are proposed. Environmental sources of nitrosyl compounds are proposed to react readily with hemoproteins to form iron-bound nitrosyl complexes. Studies to determine the nature and extent of nitrosyl complex formation in reactions of iron hemoprotens with alkyl nitrites, nitrous acid, N-nitrosamines, and other common sources of the reactive nitrosyl group are proposed. Low spin linear metalloprotein nitrosyls such as nitrosylmethemoglobin and nitrosyl-Fe (III)-horseradish peroxidase bind the nitrosyl group as the potentially reactive "NO+" ligand and are predicted to exhibit nitrosonium ion-like reactivities with nucleophiles. Investigations of the reactions of these linear nitrosylmetalloprotein adducts, defined as "reactive protein nitrosyl complexes," with biochemically significant substrates are proposed; these studies will analyze the biochemical probability for biological disruptions through reactions with organic substrates, the production of carcinogenic substances, and genetic mutations from transformations of purine and pyrimidine bases. High spin hemoprotein nitrosyl complexes such as nitrosylhemoglobin and nitrosylmyoglobin are not susceptible to reactions with nucleophiles and, because of their physiological abundance, distribution, and biological function, may serve to minimize disruptive nitrosylation reactions or function as biological storage proteins for the nitrosyl group. Investigations of nitrosyl transfer processes between high spin metalloprotein nitrosyl (nitrosyl storage proteins) and metalloproteins that can bind the nitrosyl group as a low spin adduct (reactive protein nitrosyl complexes) are proposed; these studies serve to link probable metalloprotein nitrosyl formation with potential biochemical damage from reactions of low spin nitrosyl metalloproteins. Nitrosylation reaction processes that include nitrosative deamination of primary amines and N-nitrosamine formation from reactions of secondary amines with low spin nitrosyl metalloproteins will be investigated. Related processes with metalloproteins that involve alkyl-transfer reactions to amines, alcohols, and eneamides are also proposed for investigation.